Japanese Patent Application Laid-Open NO. 2001-317333 discloses a process of regenerating the PM trapping capacity of a particulate filter while increasing the pressure inside the particulate filter by decreasing the degree of opening of an exhaust throttle valve provided in an exhaust passage downstream of the particulate filter (which process will be hereinafter referred to as the high pressure PM filter regeneration process). Japanese Utility Model Application Laid-Open No. 4-008718 and Japanese Patent Application Laid-Open No. 2003-120263 also disclose technologies related to regeneration of the PM trapping capacity of a particulate filter.